1. Field of the Invention
This invention relates to the use of powdered metal sintering or diffusion bonding to enable silicon carbide and/or rhenium alloys to coat face seal rotors, such as face seal rotors found in air turbine starter components for gas turbine engines found in aircraft or other applications.
2. Description of the Related Art
Mechanical face seals in aerospace applications operate at high rotary speeds and need high thermal conductivity rotor materials to reduce running temperatures. Aerospace face seals typically can include a metal-based disc, called a rotor, with a very flat face. Such face seals rotate while in contact or nearly in contact with a stationary, very flat carbon disc, called a stator.
Currently, one material with a high thermal conductivity typically used for rotors is silicon carbide (SiC). Silicon carbide has long been recognized as an ideal material for applications where superior attributes such as hardness and stiffness, strength and oxidation-resistance at elevated temperatures, high thermal conductivity, low coefficient of thermal expansion, and resistance to wear and abrasion are of primary value. The resiliency and utility of silicon carbide are well established in the art and silicon carbide parts are often fabricated by powder metallurgy (PM) and chemical vapor deposition (CVD). Wide use of monolithic SiC in low speed industrial equipment is acknowledgement within the seal industry that it is the “best of class” seal rotor material.
However, monolithic silicon carbide (SiC) can be brittle and is generally not used in some aerospace equipment when there are higher rotation speeds and stresses. In addition, conventional techniques of coating steel seal rotors with particulate ceramics are not capable of applying SiC because its melting and/or oxidation temperature can be exceeded by such techniques. Conventional techniques for coating steel seal rotors with ceramic include plasma spraying, high velocity oxygen fuel (HVOF), and detonation gun systems. Furthermore, fabrication of monolithic ceramics is expensive. They are difficult to machine and are susceptible to fracture as they are very notch sensitive.
Some high-speed aerospace seal applications have higher-than-preferred carbon temperatures at the rotor/stator interface. These higher temperatures can reduce the life of both the carbon stator and the face seal assembly. Although existing designs are safe and reliable, sometimes the carbon stator may fail unexpectedly and the component in which it operates, usually a gas turbine engine starter, must be replaced or repaired. Other components using carbon stators include primary propulsion aircraft engines, engine gearbox seals, engine accessories such as air turbine starters, hydraulic pumps, generators, constant speed drives, and permanent magnet alternators which must be replaced when the face seal fails. Such unplanned replacements or repairs are expensive, cause unit downtime, and increase operating costs.
In view of the foregoing disadvantages, there is a need for an improved aerospace face seal rotor that is able to better withstand the operating temperatures of aerospace applications. The present invention solves one or more of these disadvantages and satisfies a need for a better face seal and related rotor components.